Blanks for ready erection into box-like containers



27, i969 K. w. BROMLEY 3, 6, 5

BLANKS FOR READY ERECTION INTO BOX-LIKE CONTAINERS Filed April 5, 1967 Sheet I I of 4 //0 msqlFU I020 a 7 '5 p] n 0 C3'@ U Q Q Q 0 OOH G ci/li -fljp Q/ //4 P. i@/

P r iq-kifl q 9. gg w Us 05%; IS g g 30 CF03 git-D lO 8 a 21% 6: 8 I08 ./0 mnfv 2 lL/O? INVENTOR KENNETH W BROMLEY ATTY.

y 7,1969 K. w. BROMLEY I 3,446,415

BLANKS FOR READY ERECTION INTO BOX-LIKE CONTAINERS Filed April 5, 1967 Sheet Z 01 4 /02\ FIG. 2 2/ IOOA K. W. BROMLEY BLANKS FOR READY ERECTION INTO BOX-LIKE CONTAINERS Filed April 5, 1967 Sheet FIG. 6

y 19695 K'. w. BROMLEY 3,446,415

BLANKS FOR READY ERECTION INTO BOX-LIKE CONTAINERS Filed April 5, 1967 Sheet 4 of 4 FIGJZ FI6J5 United States Patent U.S. Cl. 229-30 Claims ABSTRACT OF THE DISCLOSURE A blank formed entirely of an integrally molded single mass of synthetic organic resin and capable of ready erection into a box-like container without the use of tools or external fasteners, comprising a bottom wall part, a pair of end wall parts, a pair of side wall parts, and elongated hinge parts interconnecting each of the side and end wall parts with the bottom wall part. The side wall parts are each movable between a knock-down position parallel to the plane of the bottom wall part and an erected position normal to the plane of the bottom wall part. The end wall parts are each movable between a knock-down position, an assembly position and an erected position, the end wall parts in their assembly position being superimposed upon said bottom wall part at an acute angle thereto. A pair of outwardly extending and laterally aligned bayonet pins is carried by each of the end wall parts; each of the side wall parts has a bayonet slot at each opposite end thereof, the slots in each side wall part adjacent the same end wall part being adapted to receive the bayonet pins of the associated end wall part. When the end wall parts occupy their assembly positions and the side wall parts occupy their erected positions, the laterally extending bayonet pins on the end wall parts are adapted to pass through the bayonet slots of the adjacent side wall parts. Upon movement of the end wall parts from their assembly positions to their erected positions, the engagement of the bayonet pins with the bayonet slots prevents movement of the side wall parts and the end wall parts to their knock-down positions.

The present invention relates to blanks that may be readily erected into box-like containers and to such containers that may be readily knocked-down into the blanks of which they are erected, all without the use of tools or external fasteners.

It is a general object of the invention to provide a blank of the character noted that is of one-piece construction formed entirely of an integrally molded single mass of synthetic organic resin.

Another object of the invention is to provide a blank of the character noted that is of one-piece construction formed entirely of an integrally molded single mass of synthetic organic resin, wherein the fastener means utilized to maintain the blank in an erected position are integrally molded as part of the blank and are arranged to take advantage of the elastic properties of the molding material, so that upon erection of the blank into a box-like container, the natural forces of the material tend to maintain the fastening means in a locked position.

Another object of the invention is to provide a blank of the character noted that is of simple, strong and light weight construction and that may be erected to produce a box-like container that is also of simple, strong and light-weight construction.

Another object of the invention is to provide a blank of the character noted that may be completely formed in a single stage injection molding operation in an economical manner.

A further object of the invention is to provide a blank of the character described, wherein the blank may be erected into the container and the container may be knocked-down into the blank repeatedly a great plurality of times, without damage to the blank and without impairing the utility thereof, so that a first person may ship goods in the container to a second person, and so that the second person may knock-down the container after the removal of the goods therefrom and return the blank to the first person, and so that the first person may then erect the container from the blank and again ship other goods in the container either to the second person or to a third person, whereby great economy is realized in the return of the blank to the first person and in the re-use' of the container by the first person.

A still further object of the invention is to provide a blank of the character described, wherein the same is so constructed and arranged and so dimensioned that it is particularly useful to produce upon erection thereof a container adapted to receive six stacks of cartons having four layers of cartons in each stack, with each carton adapted to contain a dozen individual eggs, wherein the container may be advantageously employed to market eggs from a chicken ranch.

Further features of the invention pertain to the particular construction and arrangement of the elements of the blank, whereby the above outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

FIGURE 1 is a plan view of a blank embodying the present invention that may be readily erected to produce the box-like container, as partially shown in FIG. 14;

FIG. 2 is a plan view of the box-like container that is produced upon erection of the blank of FIG. 1;

FIG. 3 is a side elevational view of the box-like container that is produced upon erection of the blank of FIG. 1;

FIG. 4 is an end elevational view of the box-like container that is produced upon erection of the blank of FIG. 1;

FIG. 5 is a greatly enlarged fragmentary sectional view that is partly diagrammatical, taken along the line 5-5 of FIG. 3;

FIG. 6 is a view similar to FIG. 5, showing the position of some of the elements of the blank when partially assembled;

FIG. 7 is an enlarged fragmentary side elevational view of the area designated as 7 in FIG. 3, and illustrating one of the fastening members of the invention;

FIG. 8 is a sectional view of one of the fastening members of the invention, this view being taken in the direction of the arrows along the line 8-8 of FIG. 7;

FIG. 9 is a greatly enlarged fragmentary plan View of the encircled area of the blank designated as 9 in FIG. 1, illustrating further details of the blank;

FIG. 10 is an enlarged fragmentary sectional view of the blank taken along the line 10-10 of FIG. 9;

FIG. 11 is a greatly enlarged sectional view of one of the hinge parts of the blank taken along the line 11-11 of FIG. 1;

FIG. 12 is a greatly enlarged fragmentary sectional view taken along the line 12-12 of FIG. 3;

FIG. 13 is a greatly enlarged fragmentary sectional view taken in the direction of the arrows along the lines 13-13 of FIG. 3;

FIG. 14 is a partial diagrammatic front perspective view of the box-like container that is produced upon erection of the blank of FIG. 1, as previously noted; and

FIG. is an enlarged diagrammatical end view showing a first container erected from the blank of FIG. 1, stacked on top of another similar container.

Referring now to FIG. 1 of the drawings, the blank 100 there illustrated, and embodying the features of the present invention, is capable of ready erection into a box-like container 100A, as shown in FIGS. 2, 3 and 4, without the use of tools or external fasteners. The blank 100 comprises a one-piece sheet-like construction formed entirely of an integrally molded single mass of synthetic organic resin. More particularly, the resin of which the blank 100 is molded is preferably selected from the class comprising polyolefins, polystyrene, polycarbonates, acrylics, and copolymers of vinyl chloride and vinyl acetate. As a matter of simplicity and economy, the particular polyolefin, polypropylene, is preferred, since the characteristics of polypropylene are substantially ideally suited for use in the environment in which the container 100A is employed, as explained more fully hereinafter.

Specifically, the blank 100 comprises a generally rectangular bottom part 101, a first side wall part 102, a first end wall part 103, a second side wall part 104 and a second end wall part 105, horizontally arranged in the order named about the bottom wall part 101 as illustrated in FIGURE 1. The first and second side walls 102 and 104 have substantially identical generally rectangular configurations and are disposed on the opposite sides of the bottom wall part 101; likewise the first and second end walls 103 and 105 have substantially identical rectangular configurations and are respeotively disposed at the opposite ends of the bottom wall part 101.

First and second elongated and longitudinally extending side hinge parts 102a and 104a join the opposite side edges of the bottom wall part 101 and the respectively adjacent side portions of the first and second side wall parts 102 and 104. Similarly, first and second elongated and laterally extending end hinge parts 103a and 1054:. respectively join the opposite end portions of the bottom wall part 101 and the respectively adjacent end portions of the first and second end wall parts 103 and 105 respectively.

The hinge structures 102a to 105a inclusive, are iden tical; and as illustrated in FIG. 11, the hinge structure 102a consists essentially of a narrow web of resin extending between the respectively adjacent ends of the first side wall part 102 and the edge of the bottom wall part 101. In the arrangement shown, the web 102a has a width between the bottom wall part 101 and the adjacent edge of the side wall part 102 that is approximately equal to the thickness of the side wall part 102 and the thickness of the bottom wall part 101, and the web has a thickness between the opposite sides thereof that is approximately equal to one quarter of the width thereof. This arrangement renders the hinge structure 102a, relatively foldable and bendable so as to accommodate movement of the first side wall part 102 relative to the bottom wall part 101 between a knock-down position, wherein the side wall part 102 is disposed generally in the plane of the bottom wall part 101, as shown in FIGS. 1 and 11, and an erected position, wherein the side wall pant 102 is disposed generally normal to the plane of the bottom wall part 101, as shown in FIGS. 2 through 6 and 14. The opposite side wall part 104 is similarly movable about hinge 104a between a knock-down position and an erected position normal to the bottom wall part 101, also as in the above noted figures.

Each one of the end hinge parts 103a and 105a accommodate hinged movements of the corresponding adjacent one of the end wall parts 103 and 105 between a knockdown position, wherein the end wall parts are disposed generally in the plane of the bottom wall part 101, as shown in FIG. 1, an erected position, wherein the end wall parts 103 and 105 are disopsed generally normal to the plane of the bottom wall part 101, as shown in FIGS. 2 through 6, and an assembly position, wherein the end wall p ts 103 and 105 are superimposed with r p t to the bottom wall part 101 and disposed in a plane arranged at an acute angle thereto, as partially shown in FIG. 14; whereby it will be seen that each of the end wall parts 103 and may be moved from their knock-down positions to their erected positions and into their assembly positions, and then returned from the assembly positions back into the erected positions when the respective side wall parts 102 and 104 occupy their respective erected positions.

A first pair of fastener elements 107 is respectively carried by the opposite side portions of the first end wall part 103. The fastener elements 107 each project laterally from the end wall part and are disposed in substantially lateral alignment with each other. Similarly, a second pair of fastener elements 109 is respectively carried by the opposite side portions of the second end wall part 105, the second pair of fastener elements 109 also projecting oppositely laterally from the end wall part 105 and disposed in substantial lateral alignment with each other.

A first pair of fastener members 108 is respectively carried by the end portions of the first and second side wall parts 102 and 104 that are disposed adjacent to the first end wall part 103. The first pair of fastener elements 107 is respectively arranged in cooperating relation with the first fastener members 108, so that the first fasteners elements may selectively engage and disengage the respectively cooperating ones of the first fastener members 108 when the first end wall part 103 occupies its assembly position and the side wall parts occupy their respective erected positions, as shown in FIG. 14.

It will be observed from FIGURE 1 that each of the first pair of fastener elements 107 is in the form of a bayonet pin 107a, and each of the fastener members 108 is in the form of a bayonet slot 108a, whereby it will be understood that the bayonet pins 10711 are adapted to pass through the bayonet slots 108a of the side wall parts 102 and 104 when the end wall part 103 is in the assembly position and the side wall parts 102 and 104 are each in their erected positions, as shown in FIG. 14. Upon passing the bayonet pins through the respective slots 108a, the slots accommodate selective movement of the first end wall part 103 between its assembly position and its erected position with the side wall parts 102 and 104 in their respective erected positions.

Because of the generally elastic nature of the material from which the blank is preferably molded, the natural forces acting on the hinge 103a of the end wall part 103, when the end wall part 103 is in its assembly position, is such that the hinge 103a urges the end wall part 103 toward its knock-down position, thereby effectively positioning the bayonet pins 107a well beyond the enlarged openings that are adapted to receive them in the respective bayonet slots 108a.

In a similar fashion, the second end wall part 105 also has a pair of laterally extending fastener elements 109 in the form of bayonet pins 109a carried thereby, that are adapted to be received in a second pair of fastener members 110, in the form of bayonet slots 110a, that are respectively arranged in the opposite adjacent ends of the side wall parts 102 and 104, whereby the second fastener elements 109 may selectively engage and disengage the selective cooperating ones of the second fasteners members 110, when the second end wall part 105 occupies its assembly position and the side wall parts 102 and 104 occupy their respective erected positions.

In view of the foregoing description of the blank 100, it will be readily appreciated that the same may be erected to form the box-like container shown in FIGS. 2, 3 and 14 without the use of tools or external fastener devices; and more particularly in the erection of the blank 100, the respective wall parts 101, 102, 103, 104, and 105 are positioned to form the bottom wall, side walls and end walls of the container 100A, the required positioning of the side wall parts 102 and 104 being facilitated by folding of the side wall parts along the hinge structures 102a and 104a and by the required folding of the end wall parts 103 and 105 along the respective hinge structures 103a and 105a. The end wall parts 103 and 105 are first moved into their assembly positions and then the side wall parts are moved into their erected positions; when so positioned the outwardly projecting pairs of fastener elements 107 and 109 on each end wall part 103 and 105 respectively are adapted to pass into the corresponding fastening members 108 and 110 in the side wall parts, whereupon each end wall part 103 and 105 is returned to its erected position and the blank 100 is formed into the container 100A.

While the blank 100 has been described in its simplest form, it will of course, be understood that various other structural features may be produced on the blank 100 at the time of molding same, which features may serve to strengthen the container that is formed, or provide useful purposes thereon.

Thus, for example as partially show in FIGS. 3, 7 and 8, a pair of guards 8b and 11011 is respectively carried by each of the side wall parts 102 and 104. Each of the pairs of guards 10% and 110b is directed downwardly from the adjacent lower surfaces of the side wall parts 102 and 104. The guards are each arranged in at least a partially surrounding relation with the adjacent one of the corresponding pairs of bayonet slots 108a and 110a. The pairs of guards 1081) and 11% cooperate with the respective pairs of bayonet slots 108a and 110a to protect the extreme outer ends of the corresponding pairs of bayonet pins 107a and 109a, when engaged with the corresponding bayonet slots, from damage incident to handling of the box-like container 100A erected from the blank 100.

It will also been seen that in the upper central portions of the end wall parts 103 and 105, there are respectively formed two elongated hand-grasp openings 111 and 112. Also, an outwardly directed reinforcing web 113 is respectively carried by each end wall part 103 and 105 (one web only being shown) respectively adjacent to the top portions of the hand-grasp holes 111 and 112 when the end wall parts 103 and 105 occupy their respective erected positions. This arrangement greatly facilitates the handling of the box-like container 100A and its contents in an obvious manner.

Referring now to FIGS. 1, 5, 6, 9, and 10, it will be seen that the blank 100 further comprises a plurality of interlock elements 114 carried adjacent each side portion of the bottom wall part 101; the interlock elements 114 being disposed in longitudinally spaced-apart relation with respect to each other. As shown most clearly in FIG. 10', the interlock elements 114 are each comprised of a laterally extending projection 115 carried by a corresponding side portion of the bottom wall part 101. A plurality of longitudinally spaced-apart first interlock members 116 are carried by the side portions of the respective first and second side wall parts 102 and 104 that are disposed adjacent to the corresponding side portions of the bottom wall part 101. In this case, as shown most clearly in FIGS. 5, 6, and 10, the interlock members are each essentially in the form of a slot 117 provided in the corresponding one of the side wall parts. The interlock elements or projections 115 are adapted to respectively engage the -interlock members or slots 117 when the corresponding side wall parts occupy their erected positions, as shown in FIG. 5, wherein the side .wall part 104 is shown in its erected position relative to the bottom wall part 101.

The projections 115 are adapted respectively to disengage the slots 117 when the side wall parts occupy their knock-down positions, as shown in FIGS. 6 and 10. The engagements of the projections 115 with slots 117 when the side walls are in their erected positions provides added strength in the area of the adjacent hinge parts, and thereby protects the hinge parts from damage incident to handling of the box-like container A erected from blank 100.

Referring now to FIGS. 1, 12 and 13, it will be seen that the blank 100 may further comprise a first pair of laterally extending and substantially laterally aligned ribs 118 respectively carried by the end portions of each side 'Wall part 102 and 104 disposed adjacent to the end wall part 103, and a second pair of laterally extending and substantially horizontally aligned ribs 119 respectively carried by the end portions of each side wall part disposed adjacent the second end wall part 105. Each pair of ribs 118 and 119 project upwardly from the upper surfaces of the side wall parts when the blank 100' is in its knock-down position. Each pair of ribs 118 and 119 adjacent each respective end wall part 103 and is adapted to engage the opposite side portions of the adjacent end wall part when the end wall part and the side wall parts occupy their respective erected positions, so as further to restrain the end wall parts against move ment from their erected positions into their knock-down positions.

As shown in FIGS. 3 through 6, 10 and 15, the bottom wall 101 preferably has a substantially rectangular foot 120 directed downwardly from the lower surface thereof and disposed iniwardly from the opposite sides and the opposite ends of the bottom wall part 101, whereby the foot 120 accommodates the support of the box-like container 100A erected from the blank 100 as shown in FIGS. 3 and 4. Moreover, the downwardly directed rectangular foot 120 carried by the lower surface of the bottom wall 101 of one container 100A erected from one of the blanks 100 is adapted to project into the open top of a second container 100A as shown in FIG. 15, thereby to accommodate ready stacking of the two containers respectively erected from two of the blanks 100.

The outer edge of each of the side wall parts 102 and 104 and end wall parts 103 and 105 may further be provided with a rib 121 thereon (FIG. 2 and 17) that projects upwardly from the blank when the blank is in its knock-down position. When the blank 100 is erected to the container 100A, the ribs 121 provide a rectangular frame about the top of the container to add rigidity thereto. Moreover, as shown in FIG. 15, the ribs 121 provide additional support when one container is stacked on top of another, the rectangular frame formed by the ribs 121 being adapted to receive in nesting relation the rectangular foot 120 of a second container stacked thereupon.

As noted in FIGS. 1 through 4, each of the five wall parts 101 through 105 inclusive, may have a plurality of openings 122 therethrough, the openings providing a substantially grid like structure in order to conserve the synthetic organic resin of which the blank is molded.

As partially shown in FIGS. 3 and 4, each one of the side wall parts 102 and 104 and each one of the end wall parts 103 and,105 is provided with a substantially centrally disposed flat panel 123 upon the lower surface thereof when the blank 100 is in the knock-down position. The flat central panels 123 produce a corresponding logo area on the exterior surface of the corresponding walls of the box-like container 100A when the container is erected from the blank 100.

In view of the above description of the ready erection of the blank 100 to produce the container 100A, it will be understood that the container 100A may be readily knocked-down again to form the blank 100; the knockdown steps being substantially the same as the erection steps, but in the reverse order. Thus, the blank 100 may be converted into the container 100A and the container 100A may be converted into the blank 100, as desired, and all without the use of tools or external fastening devices. Moreover, when the blank is made of the preferred materials, repeated conversion of the blank 100-container 100A will not damage the blank 100 and will not impair the utility of the container 100A. These circumstances allow a first person to erect a blank 100 into the container 100A and then use the same to ship goods to a second person. A second person may remove the goods from the container 100A, and then knock-down the same to the blank 100. A second person may then return the blank 100 to the first person; whereby the first person may again erect the blank 100 into the container 100A and then use the same to ship other goods either to the second person or to a third person. The ability to knock-down the container for return shipment effects an obvious savings in freight charges.

One use wherein a blank manufactured in accordance with the invention may advantageously be employed, is as a shipping container for four standard egg cartons, each carton being adapted to contain a dozen individual eggs, whereby the blank 100-container 100A has special utility in marketing eggs from a chicken ranch. In this example, the blank 100 is formed in a single step injection molding operation employing a single mass of polypropylene in the injection molding machine. Since eggs frequently break during transit, frequent washing of the containers is required; polypropylene is ideally suited for this purpose because of its strength, elasticity, and its resistance to acids, water and sunlight.

When used as a container for egg cartons, each of the side wall parts has the approximate dimensions of 12" by 24"; each of the end wall parts has the approximate dimensions 12" by 12'; and the bottom wall part has the approximate dimensions of 12" by 24"; the length of 24 inches accommodating six stacks of cartons with four layers of cartons in each stack.

Of course, it will be appreciated that the blank 100 is of general utility in the production of the container 100A without reference to the utility of the container 100A; however, the container 100A of the present example is especially useful for the purpose noted. The thickness of the blank 100 and the dimensions of the walls 101 to 105 inclusive, may be appropriately varied in order to produce a great variety of containers embodying the present invention.

In view of the foregoing, it is apparent that there has been provided a blank that may be readily erected into a box-like container as well as a container that may be readily knocked-down into the blank of which it is erected, all without the use of tools or external fastener devices; wherein the blank is of improved construction and arrangement, and essentially comprises a one piece construction formed entirely of an integrally molded single mass of synthetic organic resin.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein.

What is claimed is:

1. A blank capable of ready erection into a box-like container, without the use of tools or external fasteners; said blank comprising a one-piece sheet-like construction formed entirely of an integrally molded single mass of synthetic organic resin; said blank also comprising a generally rectangular bottom wall part, two substantially identical and generally rectangular side wall parts respectively disposed at opposite sides of said bottom wall part and respectively joined thereto by longitudinally extending side hinge parts, two substantially identical and generally rectangular end wall parts respectively disposed at the opposite ends of said bottom wall part and respectively joined thereto by elongated end hinge parts, each of said hinge parts accommodating hinged movements of the corresponding adjacent one of said wall parts between a knock-down position disposed generally in the plane of said bottom wall part and an erected position disposed generally normal to the plane of said bottom wall part,

two bayonet pins respectively carried by the opposite sides of each of said end wall parts and projecting laterally therefrom and disposed in substantial lateral alignment with each other, two bayonet slots respectively carried by the opposite side portions of said side wall parts, each of said slots including an enlarged assembly end disposed toward the center of the associated side wall part and a locking end offset toward the adjacent hinged part, and interlocking structures at the junctures of said bottom wall part and said side wall parts and each including a projection extending outwardly from said bottom wall part toward the adjacent side wall part and into an opening formed therein, said projection having an outwardly and downwardly inclined locking surface thereon coopcrating with an outwardly and downwardly inclined locking surface on the periphery of said opening, the engagement of said bayonet pins in the locking ends of said bayonet slots tending to move the associated side wall parts upwardly to cause firm engagement between said locking surfaces in said interlocking structures.

2. The blank set forth in claim 1, wherein each one of said four hinge parts named is in the form of a narrow web that is materially thinner than each one of said five wall parts named.

3. The blank set forth in claim 1, and further comprising a first pair of laterally extending and substantially laterally aligned ribs respectively carried by the end portions of said side wall parts that are disposed adjacent to said first end wall part and respectively projecting upwardly from the upper surfaces of said side wall parts, said first ribs respectively engaging the opposite side portions of said first end wall part when said first end wall part and said side wall parts occupy their respective erected positions so as further to restrain said first end wall part against movement from its erected position into its knock-down position, and a second pair of laterally extending and substantially laterally aligned ribs respectively carried by the end portions of said side wall parts that are disposed adjacent to said second end wall part and respectively projecting upwardly from the upper surfaces of said side wall parts, said second ribs respectively engaging the opposite side portions of said second end wall part when said second end wall part and said side wall parts occupy their respective erected positions so as further to restrain said second end wall part against movement from its erected position into its knock-down position.

4. The blank set forth in claim 1, wherein said interlocking structures comprise a plurality of first interlock elements carried by a first side portion of said bottom wall part and disposed in longitudinally spaced-apart relation with respect to each other, a plurality of longitudinally spaced-apart first interlock members carried by the side portion of a first of said side wall parts that is disposed adjacent to said first side portion of said bottom wall part, said first interlock elements respectively disengaging said first interlock members when said first side wall part occupies its knockdown position, said first interlock elements respectively engaging said first interlock members when said first side wall part occupies its erected position, whereby said first interlock elements respectively engaging said first interlock members protect the adjacent first of said hinge parts against damage incident to handling of the box-like container erected from said blank, a plurality of second interlock elements carried by the second side portion of said bottom wall part and disposed in longitudinally spaced-apart relation with respect to each other, and a plurality of longitudinally spaced-apart second interlock members carried by the side portion of the second of said side wall parts that is disposed adjacent to said second side portion of said bottom wall part, said second interlock elements respectively disengaging said second interlock members when said second side Wall part occupies its knock-down position, said second interlock elements respectively engaging said second interlock members when said second side wall part occupies its erected position, whereby said second interlock elements respectively engaging said second interlock members protect the adjacent second of said side hinge parts against damage incident to handling of the box-like container erected from said blank.

5. The blank set forth in claim 4, wherein each one of said interlock elements named is essentially in the form of a laterally extending projection carried by the corre- 10 sponding side portion of said bottom wall part, and each one of said interlock members named is essentially in the form of a slot provided in the corresponding one of said side wall parts.

1 0 References Cited UNITED STATES PATENTS 2,967,654 1/1961 Palmer 220-62 3,330,437 7/1967 Bellamy 220-6 3,360,180 12/1967 Venturi 220-30 2,714,466 8/ 1955 Killeen 220-7 FOREIGN PATENTS 1,439,717 4/1966 France. 

